Rabbis (from the Hebrew רַבִּי) are the spiritual and community leaders, as well as teachers, in Rabbinic Judaism. Originally legal scholars and judges in the Temple Judaism periods, they grew out of the legalistic and scholarly Pharisee movement of Temple Judaism after the Roman destruction of the Second Temple in 72 CE and the Roman persecution of ordained rabbis during that time period. Over the past two thousand years, rabbis and their social roles have evolved from legal scholars and judges to also include pastoral duties, sermonizing, and other community functions similar to that of a Christian minister, due to social pressures and norms from Christian cultures.

However, the core function of rabbinical duties has always been and continues to be a scholar, teacher, and adjudicator for the rest of the Jewish population. Rabbinical ordination, called סמיכה‎‎ smicha (translation: "leaning [of the hands]") [1], is done in a master-and-apprentice fashion combined with a doctorate defense--the prospective rabbi must demonstrate that they know the texts and how to interpret them to a quorum of other rabbis in order to earn the title [2]. Once the smicha has been granted, the rabbi is viewed as an authoritative source for questions on Jewish religion, Jewish law, and Jewish observance of those two (although rabbis will typically and frequently consult with other rabbis on difficult questions).

According to Jewish tradition, the chain of rabbinic smicha is unbroken back to the mythical first rabbi, Moshe Rabbeinu, a.k.a. Moses, although it is highly likely that the present day chain has been broken on multiple occasions between the modern day and its likely origins during the Temple periods. One of the likely breaks involved the above-mentioned Roman persecutions, who were actively hunting the ordained rabbis during the first four centuries CE [3], with the explicit goal of breaking the chain of the Jewish Oral Law, knowledge of which was one of the conditions of gaining smicha, and was passed teacher-to-student. During this time period, the remaining rabbis wrote down the entirety of the Oral Law in a compressed form, known as the Mishnah [4], containing rulings and discussions on situations and legal options. This then became the core text of Rabbinic Judaism, with the Gemara "unpacking" the condensed text to explore the rationals behind each ruling, with the two texts combined being referred to as the Talmud.

Education for a rabbi usually focuses on the Tanakh (the Torah and associated texts) and Talmud, as well as many other texts, opinions, analyses, and other writings accumulated over the last two and a half thousand years. The Talmud, in particular, is viewed as of particular merit in study, and is typically reviewed repeatedly and continuously throughout a rabbi's life [5] in order to apply new lessons and interpretations to the text. This makes arguing with a rabbi to be an interesting and either frustrating or entertaining experience, as the classic pastime for rabbis is literally reading over a set of two-thousand-year-old religious legal texts and eighty generations of accumulated analysis and argument of those texts, and finding logical ways and comparisons to apply the ancient laws to modern situations [6]. Particularly skilled and insightful rabbis are frequently given additional honorifics [7] and status [8] as being exceptional legal scholars--pick an argument with these at one's own risk.

In the modern era, the position of rabbi has been broadened from the traditional male-only, with Reformed, Conservative and Reconstructionist movements all embracing female rabbis, while even the more conservative Orthodox movement beginning to accept female rabbis, though the status of woman rabbis remains an ongoing debate within the larger Jewish community. There is progress even in the more restrictive Orthodox movement, in this regard, with the recent granting of smicha to women rabbis by the Shalom Hartman Institute in Israel, beginning in 2009, although the focus of that institute is explicitly the training of rabbi-teachers, not "pulpit rabbis" [9].

It should be noted that, despite surface similarities with Christian priests, rabbis are not the priests of Judaism; that status is restricted to specific bloodlines within the Jewish community, known as Kohenim (singular: kohen), ostensibly in direct patrilineal descent from Moses' brother Aaron [10]. Interestingly, there is a degree of genetic evidence for the claim of common ancestry among this group; genetic analysis shows a distinct common ancestor among a majority of those with the status of kohen, called y-chromosomal Aaron (more at Wikipedia). However, in modern Judaism, the primary functions of kohenim are strictly ceremonial, when recognized at all, mostly involving fulfilling certain roles during prayer [11], and many kohenim are not rabbis (although there is no reason or barrier for a kohen to not train as one).

↑Originally done by Moshe Rabbeinu for Joshua and the 70 elders in Numbers 27:15-23 and Deuteronomy 34:9; there's no indication that they had to undergo the defense aspect of the tradition

↑Mishnah Sanhedrin 2a lays out the requirements for the granting of smicha

↑Talmud Sanhedrin 14a According to the Talmud, which was a primary source to the persecutions, the chain of smicha was narrowed down to Rabbi Yehuda ben Bava after the Roman persecutions, and he was martyred after ordaining his five students by himself

↑[2] Daf Yomi is a relatively recent (i.e. less than 100 years old) tradition to review one page of the canonized Talmud pages per day, with the complete cycle taking about 7 and a half years to complete.

↑Occasionally helped by the imaginations of those ancient scholars, for example, rabbis looking for a precedent to cite regarding airplanes often find the hypothetical "tower flying through the air" discussed in the Babylonian Talmud Chagigah 15b to be most helpful

↑There are many examples of such titled rabbis through Jewish history; a small sample would include Rashi, Nahmanides, Maimonides, and the Chofetz Chaim, to pick a few of the more famous and influential.

↑One of particular note, especially in Orthodox Judaism, is that of posek (pl. poskim), which simply means "decider" and is viewed as authoritative by other rabbis. More at Wikipedia.